Reducing the parts count of optical systems and limiting the use of aspheric lenses in order to reduce the size and cost of the optics generally leads to greater aberrations in the optical systems and more uneven illuminance and color on the image display surface of the screen. Here, uneven illuminance means a distribution, mapped with respect to position expressed in two dimensions in an arbitrary plane, that shows highs and lows of illuminance (a non-uniform illuminance distribution), and uneven color means a distribution, mapped with respect to position expressed in two dimensions in an arbitrary plane, that shows color variations (a non-uniform chromaticity distribution).
Along with the recent increasing resolution and decreasing size of light valves has come a reduction in the spacing of their pixels. In a light valve, such as a digital micromirror device (DMD, a registered trademark), in which light is reflected by a periodic structure, diffraction occurs in addition to regular reflection. The diffraction angle pitch of the diffracted light increases with decreasing spacing of the pixels. The more finely spaced the pixels are, accordingly, the more difficult it becomes for high-order diffracted light to enter the projection optics, and the less diffracted light can be used for image projection. In addition, if there are large differences in the amount of incident light or its angle of incidence within the image formation region of the light valve (the illuminated area), differences in the amount of diffracted light in the entrance plane of the projection optics become large, resulting in increased illuminance unevenness and color unevenness on the image display surface of the screen.
In projection display devices for home theater use, because of demands for higher contrast, the optics are frequently configured with a reduced aperture diameter and a high F-number (FNO), and the amount of light is adjusted by providing baffles on the light paths in the optical system. Reducing the aperture diameter of the optical system reduces the amount of diffracted light that enters the optical system, however, which tends to increase the effect, on the image display surface of the screen, of uneven illuminance and color due to the effect of optical aberration and the effect of the finer spacing in the light valve.
To suppress illuminance unevenness and color unevenness on the image display surface of the screen, devices that use baffles having apertures with shapes that surround the beam range of light rays separated into multiple color components have been proposed (see, for example, Patent Reference 1).